Radar systems are important to the operation of various civilian and government organizations. Such organizations utilize these systems for various applications, including aircraft tracking, space object tracking (e.g. low-earth orbit), weather observation, meteorological research, unmanned aircraft systems surveillance and surface transportation.
Modern digital phased array radar systems include phased array antennas having numerous radiating elements each having a phase shifter. Beams are formed by selectively activating all or a portion of antenna elements of a given array. Scanning or steering of the beams is accomplished by shifting the phase of the signals emitted from the elements in order to provide constructive and/or destructive interference. The ability to form and steer a radar beam permits multiple functions to be performed by the same radar system. In addition to multi-function operation, these arrays tend to have a faster response time and operate at a higher resolution than existing rotating radar systems.
Modern phased array radar systems have been developed which transmit alternating or simultaneous pulses of horizontally and vertically polarized signals using, for example, arrays possessing orthogonally polarized radiating antenna elements. The orthogonal polarizations may also be used to create circularly polarized beams. As will be understood by one of ordinary skill in the art, a circularly polarized beam may be generated by creating a 90° phase shift between two orthogonal polarizations. These dual-pol radar systems, or “polarimetric” systems, offer several advantages over conventional single-pol radars. For example, in weather radar applications, by measuring along two axes, these systems have the capability of discriminating between hail and rain, estimating rainfall volume and detecting mixed precipitation.
Achieving sufficient performance (e.g. wide scan angles), high reliability and low fabrication costs in these polarimetric systems have proven difficult. Referring generally to FIGS. 1A and 1B, an exemplary polarimetric radiating element 10 according to the prior art is shown. Radiating element 10 includes a feed arrangement consisting of two pairs of vertical probes 13 embedded in a dielectric resonator configured as a puck 12 of dielectric material (e.g. ceramic). Probes 13 generate RF beams by capacitively exciting a first disk 14 arranged on a top surface of dielectric puck 12. Disk 14 in turn excites a parasitic second disk 15, which may be supported by a rod 18 extending through dielectric puck 12 and into a portion of an aluminum housing 17. Probes 13 are fed by stripline traces for generating the two orthogonal polarizations. As presently implemented, this feed arrangement utilizes circuits, such as Wilkinson combiners with embedded (i.e. buried) resistors 16 arranged in a laminated printed wire board (PWB) stack 19.
This arrangement has several drawbacks. For example, the use of buried resistors generates significant heat during operation, decreasing reliability and requiring complex thermal management considerations. In the illustrated example, housing 17 supporting dielectric puck 14 must be used as a coldplate, cooling embedded resistors 16 through conductive contact between the backside of resistors 16 and housing 17. Further, the functional accuracy of the element is dependent on the ability to precisely locate feed probes 13 within dielectric puck 12, so as to achieve a desired orientation with respect to disk 14. This alignment process can lead to further increased production costs.
Alternative structures and techniques are desired.